Laser range finders are commonly implemented based on a measurement of the round trip delay of a signal echoed by a target. For example, the round trip delay is multiplied by the speed of light (c) to determine the total back and forth distance to the target. Currently, there are various methods for determining the round trip delay. These methods may directly or indirectly determine the round trip delay.
One direct method includes measuring the time of flight (TOF) of a transmitted pulse of light. However, measuring the time of flight of a pulse requires fast electronics that limits this method to long range measurements. Some indirect methods include measuring the phase shift of a periodic signal, beat frequency of a chirped waveform, or a cross correlation of a shifted image of the transmitted signal with its echo. The indirect methods which are based on periodic signal analysis are more adapted to short or medium range distances. For example, it is possible to extract longer delays from a beat frequency determination, because the beat frequency is easier to measure using common electronics.
In the cross correlation method, the amount of phase shift of a transmitted signal that is needed to obtain the maximum correlation value represents the traveling delay of the light pulse. In other words, the round trip delay is determined by the amount the transmitted signal should to be delayed to obtain maximum correlation with its echoed signal. Such method employs a point in time comparison of a point(s) on the transmitted signal with a same point(s) on the echoed signal to determine the phase shift. The accuracy of such comparison is heavily dependant on the amount of noise contained in the echoed signal. Noise error in echoed signals are common, especially in long range transmission.
Thus, the need exists for a system and method that provide compensation for noise error in echoed signals such that more accurate phase shifts can be determined to allow accurate measurements of long distances to targets, as well as a system and method that provides additional benefits such as a simplified and cost effective system structure. Overall, the examples herein of some prior or related systems and their associated limitations are intended to be illustrative and not exclusive. Other limitations of existing or prior systems will become apparent to those of skill in the art upon reading the following Detailed Description.
The headings provided herein are for convenience only and do not necessarily affect the scope or meaning of the claimed invention.
In the drawings, the same reference numbers and any acronyms identify elements or acts with the same or similar structure or functionality for ease of understanding and convenience. To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the Figure number in which that element is first introduced (e.g., element 202 is first introduced and discussed with respect to FIG. 2).